A reset to factory settings should be used only as a last resort when troubleshooting. All personal data, files, settings and installed apps will be removed and cannot be recovered.
Also, please note that in order to connect your controller or remote after a factory reset, the on-screen instructions will not be valid. Instead, follow these instructions: http://shield.nvidia.com/connect.
Note: By performing a factory data reset, all data will be wiped from your SHIELD TV. Data associated with your Google account can be recovered. Any device settings will also be removed.
Note: For SHIELD TV Pro, full reset may take up to 2 hours. All personal data will be erased from the 500 GB hard drive.
RESET THROUGH SETTINGS
To reset your SHIELD to factory settings, follow these steps:
From the Home screen, navigate to the Settings menu.
Select Device Preferences
Then select Erase everything to confirm and reset your device.